How to Fix Broken Window Weatherstripping: Step-by-Step Guide

A drafty window is one of the most common sources of energy waste in a home, and the fix is often a $10 roll of weatherstripping and an hour of your time.

A drafty window is one of the most common sources of energy waste in a home, and the fix is often a $10 roll of weatherstripping and an hour of your time. Whether you have a double-hung window rattling in a winter wind or a casement that no longer closes with a tight seal, this guide covers the most common weatherstripping types, how to identify which is failing, and how to install the replacement correctly.

What You Need

• V-strip tension seal weatherstripping (for sash channels)
• EPDM rubber foam weatherstripping tape (for head and sill)
• Pile weatherstripping (for older double-hung sash channels)
• Utility knife or scissors
• Tape measure
• Putty knife or flathead screwdriver (for removing old strips)
• Rubbing alcohol and rags (for surface prep)
• Hammer and finishing nails (for V-strip if nail-in type)

Step 1 — Identify the Failing Weatherstripping Location

Different parts of a window use different weatherstripping. Before buying materials, identify exactly where the air is getting in.

Top rail (head jamb): The horizontal strip at the top of the upper sash. Usually foam tape or bulb seal. Check by feeling for air with the window closed.

Bottom rail (sill): The horizontal seal at the bottom of the lower sash against the window stool. High-wear area because the sash presses down on it with each closing.

Sash channels (vertical sides): The slots the sash slides in. V-strip or pile weatherstripping lives here in double-hung windows. This is the most common location for drafts in older windows.

Meeting rail: Where the upper and lower sash meet in the middle of a double-hung window. Foam tape or a meeting rail seal goes here.

Casement perimeter: The full perimeter of a casement or awning window uses a compression gasket molded into the frame.

Step 2 — Remove Old Weatherstripping

Old weatherstripping must be fully removed before installing new material. Patching over degraded or flattened material will not create a proper seal.

1. For adhesive-backed foam tape, peel it away from the frame. Use a putty knife to scrape off any remaining adhesive.
2. For V-strip nailed into the channel, use a flathead screwdriver to pry up the ends and pull out the strip along with its nails.
3. For pile strips in sash channels, slide them out of their kerf (slot). Older units may have the pile glued in place — scrape it out with a putty knife.
4. For casement gaskets, pull the old gasket out of its channel groove around the perimeter.

Clean the surface thoroughly with rubbing alcohol on a rag. Adhesive-backed products will not bond to dirty, dusty, or oily surfaces.

Step 3 — Install V-Strip in Sash Channels

V-strip (also called tension seal) is a folded strip of thin metal or plastic that presses against the sash side as it slides, creating a spring-tension seal. It is the most effective and longest-lasting option for sash channels.

1. Measure the height of each sash channel and cut V-strip to length with scissors or tin snips.
2. Slide the V-strip into the channel with the open side of the V facing out (toward the sash). The folded spine rides along the channel wall.
3. For self-adhesive V-strip, peel the backing and press firmly into the channel.
4. For nail-in V-strip, hammer small finishing nails through the pre-punched holes every 2 to 3 inches.
5. Open and close the window to confirm the sash slides smoothly. If it sticks, the V-strip may be over-tensioned — flatten it slightly by pressing a putty knife along the open edge.

Step 4 — Install Foam Tape at Head and Sill

For the top rail and sill (bottom of the lower sash), adhesive-backed EPDM foam tape is the right product. It compresses when the sash closes and springs back when the window opens.

1. Measure the width of each location and cut the tape to length with scissors.
2. Peel the backing from 6 inches of tape at a time and press it firmly onto the frame surface that the sash will contact when closed.
3. For the sill, install the tape on the top face of the stool (the surface the lower sash rests on when closed).
4. For the head jamb, install the tape on the underside of the head stop.
5. Close the window and check that the sash compresses the foam visibly. If there is no compression, the foam is too thin — use a thicker profile.

Step 5 — Install Meeting Rail Seal

The meeting rail is where the upper and lower sash meet when both are closed. A strip of foam tape or a dedicated meeting rail seal installed on the bottom face of the upper sash’s bottom rail seals this gap.

Apply the foam tape along the bottom of the upper sash rail. This surface is easy to access when the lower sash is raised.

Step 6 — Replacing Casement Window Gaskets

Casement window seals are a continuous gasket that runs in a groove around the frame perimeter. Replacement gaskets are available in profiles matching major window manufacturers.

1. Note the profile shape of the old gasket before removing it — photograph it if possible, or take it to the hardware store to match the cross-section.
2. Pull the old gasket out of its groove around the full perimeter.
3. Starting at a corner, press the new gasket into the groove, working around the perimeter. Most compression gaskets press in with finger pressure; some require a roller.
4. Cut the gasket to length at the finishing corner and press the end in.
5. Close and latch the window to test the seal.

Step 7 — Test the Seal

With all new weatherstripping installed, perform a final draft test. On a cold or windy day, hold a lit candle near all four edges of the closed window. Any flame movement indicates a remaining gap. Pay particular attention to corners, where strips often leave small gaps.

For corners where two strips of weatherstripping meet, press a small piece of foam tape across the joint to fill the gap.

Long-Term Maintenance

• Inspect weatherstripping every fall before heating season and every spring before cooling season.
• Clean foam weatherstripping gently with a damp cloth — do not use solvents, which degrade the foam.
• If a window is difficult to close after new weatherstripping is installed, the strip may be too thick for the gap. Replace it with a thinner profile.
• Caulk the exterior perimeter of each window frame every 5 years to seal the joint between the frame and the wall — weatherstripping handles the movable joint, caulk handles the fixed joint.

Related Reading

• How to Fix a Broken Window Screen
• How to Winterize Your Home
• How to Reduce Energy Bills with DIY Home Improvements
• How to Fix a Broken Door Sweep — seal the gap at the door bottom alongside window weatherstripping